Surfactant-polymer composition for substantially solid-free water based drilling, drill-in, and completion fluids

Abstract

Water based drilling, drill-in, and completion fluids comprising surfactant-polymer blends that are effective to generate effective rheology comprising low shear rate viscosity and effective fluid loss control properties. The water based fluids preferably are substantially solid free.

1. A water-based drilling fluid comprising:
 an aqueous base; 
 about 7.5 lb./bbl. 50/50 wt. % modified xanthan polysaccharide and synthetically modified starch; and, 
 about 2 lb./bbl. surfactant in association with said water soluble polymer; 
 wherein said water soluble polymer, said surfactant, and said association provide said water-based drilling fluid with effective rheology and fluid loss control properties comprising low shear viscosity. 
 
     
     
       2. The water-based drilling fluid of  claim 1  wherein said surfactant is selected from the group consisting of alkyl sulfates, alkyl ether sulfates, alkyl sulfonates, ethoxylated esters, ethoxylated glycoside esters, alcohol ethers, and phosphated esters comprising about 8 to about 18 carbon atoms, alkali metal salts thereof, and combinations thereof. 
     
     
       3. The water-based drilling fluid of  claim 1  wherein said surfactant is selected from the group consisting of alkyl sulfates and alkyl ether sulfates. 
     
     
       4. The water-based drilling fluid of  claim 1  wherein said surfactant comprises an alkyl ether sulfate. 
     
     
       5. The water-based drilling fluid of  claim 1  wherein said surfactant is sodium tridecyl ether sulfate. 
     
     
       6. The water-based drilling fluid of  claim 1  wherein said low shear viscosity is about 70,000 cP or more upon exposure to 0.3 rpm, measured with a Brookfield viscometer at 75° F. 
     
     
       7. The water-based drilling fluid of  claim 1  wherein said low shear viscosity is about 100,000 cP or more upon exposure to 0.3 rpm, measured with a Brookfield viscometer at 75° F. 
     
     
       8. The water-based drilling fluid of  claim 3  wherein said low shear viscosity is about 70,000 cP or more upon exposure to 0.3 rpm, measured with a Brookfield viscometer at 75° F. 
     
     
       9. The water-based drilling fluid of  claim 4  wherein said low shear viscosity is about 70,000 cP or more upon exposure to 0.3 rpm, measured with a Brookfield viscometer at 75° F. 
     
     
       10. The water-based drilling fluid of  claim 5  wherein said low shear viscosity is about 70,000 cP or more upon exposure to 0.3 rpm, measured with a Brookfield viscometer at 75° F. 
     
     
       11. The water-based drilling fluid of  claim 1  further comprising a concentration of non-toxic water emulsifiable material as an internal phase. 
     
     
       12. The water-based drilling fluid of  claim 11  wherein said concentration is from about 2 to about 20 vol. %. 
     
     
       13. The water-based drilling fluid of  claim 1  wherein said fluid consists essentially of additives other a solid bridging agent. 
     
     
       14. The water-based drilling fluid of  claim 3  wherein said fluid consists essentially of additives other than a solid bridging agent. 
     
     
       15. The water-based drilling fluid of  claim 6  wherein said fluid consists essentially of additives other than a solid bridging agent. 
     
     
       16. The water-based drilling fluid of  claim 8  wherein said fluid consists essentially of additives other than a solid bridging agent. 
     
     
       17. The water-based drilling fluid of  claim 9  wherein said fluid consists essentially of additives other than a solid bridging agent. 
     
     
       18. The water-based drilling fluid of  claim 1  wherein said effective fluid l6ss control properties comprise a fluid loss of about 5 ml./30 min. or less using the standard dynamic filtration fluid loss test. 
     
     
       19. The water-based drilling fluid of  claim 13  wherein said effective fluid loss control properties comprise a fluid loss of about 5 ml./30 min. or less using the standard dynamic filtration fluid loss test. 
     
     
       20. The water-based drilling fluid of  claim 14  wherein said effective fluid loss control properties comprise a fluid loss of about 5 ml./30 min. or less using the standard dynamic filtration fluid loss test. 
     
     
       21. The water based drilling fluid of  claim 1  wherein said surfactant produces a reduced surface tension of said water based drilling fluid. 
     
     
       22. The water based drilling fluid of  claim 21  wherein said reduced surface tension of said water based drilling fluid is from about 25 to about 40 nN/m. 
     
     
       23. The water based drilling fluid of  claim 13  wherein said surfactant produces a reduced surface tension of said water based drilling fluid. 
     
     
       24. The water based drilling fluid of  claim 23  wherein said reduced surface tension of said water based drilling fluid is from about 25 to about 40 nN/m. 
     
     
       25. The water based drilling fluid of  claim 18  wherein said surfactant produces a reduced surface tension of said water based drilling fluid. 
     
     
       26. The water based drilling fluid of  claim 25  wherein said reduced surface tension of said water based drilling fluid is from about 25 to about 40 nN/m. 
     
     
       27. A water-based drilling fluid comprising:
 an aqueous base; 
 about 7.5 lb./bbl. water soluble polymer comprising xanthan polysaccharides; and, 
 about 2 lb./bbl. surfactant in association with said water soluble polymer, said surfactant being selected from the group consisting of alkyl sulfates and alkyl ether sulfates; 
 said water based drilling fluid consisting essentially of additives other than a solid bridging agent; 
 wherein said water soluble polymer, said surfactant, and said association provide said water-based drilling fluid with effective rheology and fluid loss control properties comprising low shear viscosity of about 70,000 cP or more upon exposure to 0.3 rpm, measured with a Brookfield viscometer at 75° F. 
 
     
     
       28. A water-based drilling fluid comprising:
 about 7.5 lb./bbl. water soluble polymer comprising from about 40 to about 60 wt. % xanthan polysaccharide and from about 40 to about 60 wt. % synthetically modified starch comprising one or more functional groups selected from the group consisting of carboxymethyl, propylene glycol, and epichlorohydrin functional groups; 
 about 2 lb./bbl. sodium tridecyl ether sulfate in association with said water soluble polymer; and 
 a concentration of a non-toxic water emulsifiable material as an internal phase; 
 wherein said water soluble polymer, said surfactant, and said association provide said water-based drilling fluid with effective rheology and fluid loss control properties comprising low shear viscosity. 
 
     
     
       29. The water-based drilling fluid of  claim 28  wherein said water soluble polymer is selected from the group consisting of water soluble starches and modified versions thereof, water-soluble polysaccharides and modified versions thereof, water-soluble celluloses and modified versions thereof, water soluble polyacrylamides and copolymers thereof, and combinations thereof. 
     
     
       30. The water-based drilling fluid of  claim 28  wherein said water soluble polymer is a combination comprising about 50 wt. % xanthan polysaccharide and about 50 wt. % synthetically modified starch comprising one or more functional groups selected from the group consisting of carboxymethyl, propylene glycol, and epichlorohydrin functional groups. 
     
     
       31. A water-based drilling fluid comprising:
 an aqueous base; 
 about 7.5 lb./bbl. of water soluble polymer comprising a combination of about 50 wt. % xanthan polysaccharide and about 50 wt. % synthetically modified starch comprising one or more functional groups selected from the group consisting of a carboxymethyl group, a propylene glycol group, and an epichlorohydrin functional group; 
 about 2 lb./bbl. sodium tridecyl ether sulfate; 
 wherein said water soluble polymer, said surfactant, and said association provide said water-based drilling fluid with effective rheology and fluid loss control properties comprising low shear rate viscosity; and 
 wherein said water-based fluid consists essentially of additives other than solid bridging agents. 
 
     
     
       32. The water based drilling fluid of  claim 31  further comprising a concentration of a non-toxic water emulsifiable material as an internal phase. 
     
     
       33. The water-based drilling fluid of  claim 32  wherein said non-toxic water emulsifiable material is a water insoluble material selected from the group consisting of olefins, paraffins, water insoluble glycols, water insoluble esters, water insoluble Fischer-Tropsch reaction products, and combinations thereof. 
     
     
       34. The water-based drilling fluid of  claim 31  further comprising an alkali metal salt of a compound selected from the group consisting of a thiosulfate and a thiosulfonate. 
     
     
       35. The water-based drilling fluid of  claim 32  further comprising an alkali metal salt of a compound selected from the group consisting of a thiosulfate and a thiosulfonate. 
     
     
       36. The water-based drilling fluid of  claim 31  wherein said water soluble polymer comprises 50/50 wt. % modified xanthan polysaccharide and synthetically modified starch. 
     
     
       37. The water-based drilling fluid of  claim 32  wherein said water soluble polymer comprises 50/50 wt. % modified xanthan polysaccharide and synthetically modified starch. 
     
     
       38. The water-based drilling fluid of  claim 34  wherein said water soluble polymer comprises 50/50 wt. % modified xanthan polysaccharide and synthetically modified starch. 
     
     
       39. The water-based drilling fluid of  claim 35  wherein said water soluble polymer comprises 50/50 wt. % modified xanthan polysaccharide and synthetically modified starch. 
     
     
       40. The water-based drilling fluid of  claim 31  wherein said low shear rate viscosity is about 70,000 cP or more upon exposure to 0.3 rpm, measured with a Brookfield viscometer at 75° F. 
     
     
       41. The water-based drilling fluid of  claim 32  wherein said low shear rate viscosity is about 100,000 cP or more upon exposure to 0.3 rpm, measured with a Brookfield viscometer at 75° F. 
     
     
       42. The water-based drilling fluid of  claim 33  wherein said low shear rate viscosity is about 70,000 cP or more upon exposure to 0.3 rpm, measured with a Brookfield viscometer at 75° F. 
     
     
       43. The water-based drilling fluid of  claim 34  wherein said low shear rate viscosity is about 70,000 cP or more upon exposure to 0.3 rpm, measured with a Brookfield viscometer at 75° F. 
     
     
       44. The water-based drilling fluid of  claim 35  wherein said low shear rate viscosity is about 70,000 cP or more upon exposure to 0.3 rpm, measured with a Brookfield viscometer at 75° F. 
     
     
       45. The water-based drilling fluid of  claim 32  wherein said concentration is from about 2 to about 20 vol. %. 
     
     
       46. The water-based drilling fluid of  claim 45  wherein said effective fluid loss control properties comprise a fluid loss of about 5 ml./30 rpm, or less using the standard dynamic filtration fluid loss test. 
     
     
       47. A water-based drilling fluid comprising:
 an aqueous base comprising a concentration of about 20 vol. % or less non-toxic water emulsifiable material, as an internal phase; 
 a quantity of water soluble polymer comprising polymers selected from the group consisting of synthetically modified starches having a weight average molecular weight of from about 200,000 to about 2,500,000, said water soluble polymer further comprising xanthan polysaccharides; and, 
 an amount of surfactant in association with said water soluble polymer, said surfactant being selected from the group consisting of alkyl sulfates, alkyl ether sulfates, alkyl sulfonates, ethoxylated esters, ethoxylated glycoside esters, alcohol ethers, and phosphated esters comprising about 8 to about 18 carbon atoms, alkali metal salts thereof, and combinations thereof; 
 wherein said quantity, said amount, and said association provide said water based drilling fluid with effective rheology and fluid loss control properties comprising a low shear rate viscosity of about 70,000 cP or more upon exposure to 0.3 rpm, measured with a Brookfield viscometer at 75° F. 
 
     
     
       48. The water-based drilling fluid of  claim 47  wherein said effective rheology and fluid loss control properties comprise a low shear rate viscosity of about 100,000 cP or more upon exposure to 0.3 rpm, measured with a Brookfield viscometer at 75° F. 
     
     
       49. The water-based drilling fluid of  claim 47  wherein said surfactant is selected from the group consisting of alkyl sulfates and alkyl ether sulfates. 
     
     
       50. The water-based drilling fluid of  claim 47  wherein said surfactant comprises an alkyl ether sulfate. 
     
     
       51. The water-based drilling fluid of  claim 48  wherein said surfactant is selected from the group consisting of alkyl sulfates and alkyl ether sulfates. 
     
     
       52. The water-based drilling fluid of  claim 48  wherein said surfactant comprises an alkyl ether sulfate. 
     
     
       53. The water-based drilling fluid of  claim 48  wherein said fluid consists essentially of additives other than a solid bridging agent. 
     
     
       54. The water-based drilling fluid of  claim 51  wherein said fluid consists essentially of additives other than a solid bridging agent. 
     
     
       55. The water-based drilling fluid of  claim 52  wherein said fluid consists essentially of additives other than a solid bridging agent. 
     
     
       56. The water-based drilling fluid of  claim 47  wherein said effective fluid loss control properties comprise a fluid loss of about 5 ml./30 min. or less using the standard dynamic filtration fluid loss test. 
     
     
       57. The water-based drilling fluid of  claim 51  wherein said effective fluid loss control properties comprise a fluid loss of about 5 ml./30 min. or less using the standard dynamic filtration fluid loss test. 
     
     
       58. The water-based drilling fluid of  claim 55  wherein said effective fluid lass control properties comprise a fluid loss of about 5 ml./30 min. or less using the standard dynamic filtration fluid loss test. 
     
     
       59. The water-based drilling fluid of  claim 55  wherein said effective fluid loss control properties comprise a fluid loss of about 1 ml./30 min. or less using the standard dynamic filtration fluid loss test. 
     
     
       60. The water based drilling fluid of  claim 47  wherein said surfactant produces a reduced surface tension of said water based drilling fluid. 
     
     
       61. The water based drilling fluid of  claim 1  wherein said reduced surface tension of said water based drilling fluid is from about 25 to about 40 nN/m. 
     
     
       62. The water-based drilling fluid of  claim 55  wherein said concentration is from about 2 to about 20 vol. %. 
     
     
       63. The water-based drilling fluid of  claim 47  wherein said water soluble polymer comprises one or more polymers selected from the group consisting of modified polysaccharides having a weight average molecular weight of about 500,000 to about 42,500,000. 
     
     
       64. The water-based drilling fluid of  claim 47  wherein said water soluble polymer comprises one or more polymers selected from the group consisting of modified polysaccharides having a weight average molecular weight of about from about 700,000 to about 1,200,000. 
     
     
       65. The water-based drilling fluid of  claim 47  wherein said water soluble polymer comprises polymers selected from the group consisting of synthetically modified starches having a weight average molecular weight of from about 600,000 to about 1,000,000. 
     
     
       66. The water-based drilling fluid of  claim 63  wherein said synthetically modified polysaccharides comprise a functional group selected from the group consisting of a carboxymethyl group, a propylene glycol group, and an epichlorohydrin group. 
     
     
       67. The water-based drilling fluid of  claim 47  wherein said synthetically modified starches comprise a functional group selected from the group consisting of a carboxymethyl group, a propylene glycol group, and an epichlorohydrin group. 
     
     
       68. The water-based drilling fluid of  claim 47  having a density of about 7.9 lb./gal. or more. 
     
     
       69. A water-based drilling fluid comprising:
 an aqueous base; 
 a quantity of water soluble polymer comprising one or more polymers selected from the group consisting of synthetically modified starches having a weight average molecular weight of from about 200,000 to about 2,500,000, said water soluble polymer further comprising xanthan polysaccharide; 
 an amount of surfactant in association with said water soluble polymer, said surfactant being selected from the group consisting of alkyl sulfates, alkyl ether sulfates, alkyl sulfonates, ethoxylated esters, ethoxylated glycoside esters, alcohol ethers, and phosphated esters comprising about 8 to about 18 carbon atoms, alkali metal salts thereof, and combinations thereof; 
 wherein said quantity, said amount, and said association provide said water-based drilling fluid with effective rheology and fluid loss control properties; and 
 a concentration of about 20 vol. % or less non-toxic water emulsifiable material as an internal phase, said surfactant being effective to emulsify said water emulsifiable material and to produce emulsion droplets having an average diameter of about 30 microns or less. 
 
     
     
       70. The water-based drilling fluid of  claim 69  wherein said surfactant is selected from the group consisting of alkyl sulfates and alkyl ether sulfates. 
     
     
       71. The water-based drilling fluid of  claim 69  wherein said surfactant comprises an alkyl ether sulfate. 
     
     
       72. The water-based drilling fluid of  claim 69  wherein said surfactant is sodium tridecyl ether sulfate. 
     
     
       73. The water-based drilling fluid of  claim 69  wherein said surfactant is effective to emulsify said water emulsifiable material and to produce emulsion droplets having an average diameter of about 20 microns or less. 
     
     
       74. The water-based drilling fluid of  claim 69  wherein said surfactant is effective to emulsify said water emulsifiable material and to produce emulsion droplets having an average diameter of about 15 microns or less. 
     
     
       75. The water-based drilling fluid of  claim 69  wherein said surfactant is effective to emulsify said water emulsifiable material and to produce emulsion droplets having an average diameter of about 5 microns or less. 
     
     
       76. The water-based drilling fluid of  claim 69  wherein said effective rheology and fluid loss control properties comprise a low shear rate viscosity of about 70,000 cP or more upon exposure to 0.3 rpm, measured with a Brookfield viscometer 75° F. 
     
     
       77. The water-based drilling fluid of  claim 69  wherein said concentration is, from about 2 to about 20 vol. %. 
     
     
       78. The water-based drilling fluid of  claim 69  wherein said concentration is about 5 vol. %. 
     
     
       79. The water-based drilling fluid of  claim 73  wherein said concentration is about 5 vol. %. 
     
     
       80. The water-based drilling fluid of  claim 69  wherein said non-toxic water emulsifiable material is a water insoluble material selected from the group consisting of olefins, paraffins, water insoluble glycols, water insoluble esters, water insoluble Fischer-Tropsch reaction products, and combinations thereof. 
     
     
       81. The water-based drilling fluid of  claim 69  wherein said water emulsifiable material is a water insoluble material selected from the group consisting of olefins, paraffins, water insoluble glycols, and combinations thereof. 
     
     
       82. The water-based drilling fluid of  claim 73  wherein said water emulsifiable material is a water insoluble material selected from the group consisting of olefins, paraffins, water insoluble glycols, and combinations thereof. 
     
     
       83. The water-based drilling fluid of  claim 69  wherein said fluid consists essentially of additives other a solid bridging agent. 
     
     
       84. The water-based drilling fluid of  claim 73  wherein said fluid consists essentially of additives other than a solid bridging agent. 
     
     
       85. The water-based drilling fluid of  claim 79  wherein said fluid consists essentially of additives other than a solid bridging agent. 
     
     
       86. The water-based drilling fluid of  claim 69  wherein said effective fluid loss control properties comprise a fluid loss of about 5 ml./30 min. or less using the standard dynamic filtration fluid loss test. 
     
     
       87. The water-based drilling fluid of  claim 75  wherein said effective fluid loss control properties comprise a fluid loss of about 5 ml./30 min. or less using the standard dynamic c filtration fluid loss test. 
     
     
       88. The water-based drilling fluid of  claim 69  wherein said effective fluid loss control properties comprise a fluid loss of about 1 ml./30 min. or less using the standard dynamic filtration fluid loss test. 
     
     
       89. The water-based drilling fluid of  claim 75  wherein said effective fluid loss control properties comprise a fluid loss of about 1 ml./30 min. or less using the standard dynamic filtration fluid loss test. 
     
     
       90. The water based drilling fluid of  claim 69  wherein said surfactant produces a reduced surface tension of said water based drilling fluid. 
     
     
       91. The water based drilling fluid of  claim 90  wherein said reduced surface tension of said water based drilling fluid is from about 25 to about 40 nN/m. 
     
     
       92. The water based drilling fluid of  claim 73  wherein said surfactant produces a reduced surface tension of said water based drilling fluid. 
     
     
       93. The water based drilling fluid of  claim 92  wherein said reduced surface tension of said water based drilling fluid is from about 25 to about 40 nN/m. 
     
     
       94. The water-based drilling fluid of  claim 69  wherein said water soluble polymer comprises one or more polymers selected from the group consisting of modified polysaccharides having a weight average molecular weight of about 500,000 to about 2,500,000. 
     
     
       95. The water-based drilling fluid of any of  claims 69  wherein said water soluble polymer comprises one or more polymers selected from the group consisting of modified polysaccharides having a weight average molecular weight of about from about 700,000 to about 1,200,000. 
     
     
       96. The water-based drilling fluid of  claim 69  wherein said water soluble polymer comprises one or more polymers selected from the group consisting of modified polysaccharides having a weight average molecular weight of about 600,000 to about 1,000,000. 
     
     
       97. The water-based drilling fluid of  claim 69  wherein said synthetically modified starches comprise a functional group selected from the group consisting of a carboxymethyl group, a propylene glycol group, and an epichlorohydrin group. 
     
     
       98. The water-based drilling fluid of  claim 94  wherein said synthetically modified polysaccharides comprise a functional group selected from the group consisting of a carboxymethyl group, a propylene glycol group, and an epichlorohydrin group. 
     
     
       99. A water-based drilling fluid comprising:
 an aqueous base comprising a concentration of about 20 vol. % or less non-toxic water emulsifiable material as an internal phase; 
 about 2 lb./bbl. or more water soluble polymer comprising one or more polymers selected from the group consisting of synthetically modified starches having a weight average molecular weight of from about 200,000 to about 2,500,000, said water soluble polymers further comprising xanthan polysaccharides; and, 
 about 0.2 lb./bbl. or more surfactant in association with said water soluble polymer, said surfactant being selected from the group consisting of alkyl sulfates, alkyl ether sulfates, alkyl sulfonates, ethoxylated esters, ethoxylated glycoside esters, alcohol ethers, and phosphated esters comprising about 8 to about 18 carbon atoms, alkali metal salts thereof, and combinations thereof; 
 wherein said water soluble polymer, said surfactant, and said association provide said water-based drilling fluid with effective rheology and fluid loss control properties. 
 
     
     
       100. The water-based drilling fluid of  claim 69  wherein said surfactant is selected from the group consisting of alkyl sulfates and alkyl ether sulfates. 
     
     
       101. The water-based drilling fluid of  claim 99  wherein said surfactant comprises an alkyl ether sulfate. 
     
     
       102. The water-based drilling fluid of  claim 99  wherein said surfactant is sodium tridecyl ether sulfate. 
     
     
       103. The water-based drilling fluid of  claim 99  wherein said effective rheology and fluid loss control properties comprise a low shear rate viscosity of about 70,000 cP or more upon exposure to 0.3 rpm, measured with a Brookfield viscometer at 75° F. 
     
     
       104. The water-based drilling fluid of  claim 99  wherein said concentration is from about 2 to about 20 vol. %. 
     
     
       105. The water-based drilling fluid of  claim 101  wherein said concentration is from about 2 to about 20 vol. %. 
     
     
       106. The water-based drilling fluid of  claim 99  wherein said fluid consists essentially of additives other a solid bridging agent. 
     
     
       107. The water-based drilling fluid of  claim 101  wherein said fluid consists essentially of additives other than a solid bridging agent. 
     
     
       108. The water-based drilling fluid of  claim 102  wherein said fluid consists essentially of additives other than a solid bridging agent. 
     
     
       109. The water-based drilling fluid of  claim 99  wherein said effective fluid loss control properties comprise a fluid loss of about 5 ml./30 min. or less using the standard dynamic filtration fluid loss test. 
     
     
       110. The water-based drilling fluid of  claim 108  wherein said effective fluid loss control properties comprise a fluid loss of about 5 ml./30 min. or less using the standard dynamic filtration fluid loss test. 
     
     
       111. The water based drilling fluid of  claim 99  wherein said surfactant produces a reduced surface tension of said water based drilling fluid. 
     
     
       112. The water based drilling fluid of  claim 111  wherein said reduced surface tension of said water based drilling fluid is from about 25 to about 40 nN/m. 
     
     
       113. The water based drilling fluid of  claim 108  wherein said surfactant produces a reduced surface tension of said water based drilling fluid. 
     
     
       114. The water based drilling fluid of  claim 113  wherein said reduced surface tension of said water based drilling fluid is from about 25 to about 40 nN/m. 
     
     
       115. The water based drilling fluid of  claim 103  wherein said surfactant produces a reduced surface tension of said water based drilling fluid. 
     
     
       116. The water based drilling fluid of  claim 115  wherein said reduced surface tension of said water based drilling fluid is from about 25 to about 40 nN/m. 
     
     
       117. The water-based drilling fluid of  claim 99  wherein said water soluble polymer comprises one or more polymers selected from the group consisting of modified polysaccharides having a weight average molecular weight of about 500,000 to about 2,500,000. 
     
     
       118. The water-based drilling fluid of  claim 99  wherein said water soluble polymer comprises one or more polymers selected from the group consisting of modified polysaccharides having a weight average molecular weight of from about 700,000 to about 1,200,000. 
     
     
       119. The water-based drilling fluid of  claim 99  wherein said water soluble polymer comprises one or more polymers selected from the group consisting of synthetically modified starches having a weight average molecular weight of from about 600,000 to about 1,000,000. 
     
     
       120. The water-based drilling fluid of  claim 99  wherein said synthetically modified starches comprise a functional group selected from the group consisting of a carboxymethyl group, a propylene glycol group, and an epichlorohydrin group. 
     
     
       121. The water-based drilling fluid of  claim 117  wherein said synthetically modified polysaccharides comprise a functional group selected from the group consisting of a carboxymethyl group, a propylene glycol group, and an epichlorohydrin group. 
     
     
       122. The water-based drilling fluid of  claim 99  wherein said water soluble polymer comprises about 50/50 wt. % modified xanthan polysaccharide and synthetically modified starch. 
     
     
       123. The water-based drilling fluid of  claim 108  wherein said water soluble polymer comprises about 50/50 wt. % modified xanthan polysaccharide and synthetically modified starch. 
     
     
       124. A water-based drilling fluid comprising:
 an aqueous base comprising a concentration of non-toxic water emulsifiable material as an internal phase; 
 a blend of water soluble polymers comprising from about 10 wt. % to about 90 wt. % modified polysaccharide and from about 10 wt. % to about 90 wt. % synthetically modified starch; and, 
 an amount of surfactant in association with said water soluble polymer, said surfactant being selected from the group consisting of alkyl sulfates, alkyl ether sulfates, alkyl sulfonates, ethoxylated esters, ethoxylated glycoside esters, alcohol ethers, and phosphated esters comprising about 8 to about 18 carbon atoms, alkali metal salts thereof, and combinations thereof; 
 wherein said quantity, said amount, and said association provide said water based drilling fluid with effective rheology and fluid loss control properties comprising a low shear rate viscosity of about 70,000 cP or more upon exposure to 0.3 rpm, measured with a Brookfield viscometer at 75° F. 
 
     
     
       125. The water-based drilling fluid of  claim 124  wherein said effective rheology and fluid loss control properties comprise a low shear rate viscosity of about 100,000 cP or more upon exposure to 0.3 rpm, measured with a Brookfield viscometer at 75° F. 
     
     
       126. The water-based drilling fluid of  claim 124  wherein said surfactant is selected from the group consisting of alkyl sulfates and alkyl ether sulfates. 
     
     
       127. The water-based drilling fluid of  claim 124  wherein said surfactant comprises an alkyl ether sulfate. 
     
     
       128. The water-based drilling fluid of  claim 124  wherein said fluid consists essentially of additives other than a solid bridging agent. 
     
     
       129. The water-based drilling fluid of  claim 124  wherein said effective fluid loss control properties comprise a fluid loss of about 5 ml./30 min. or less using the standard dynamic filtration fluid loss test. 
     
     
       130. The water-based drilling fluid of  claim 124  wherein said effective fluid loss control properties comprise a fluid loss of about 1 ml./30 min. or less using the standard dynamic filtration fluid loss test. 
     
     
       131. The water-based drilling fluid of  claim 124  wherein said water modified polysaccharides have a weight average molecular weight of about 500,000 to about 2,500,000. 
     
     
       132. The water-based chilling fluid of  claim 124  wherein said water soluble polymer comprises one or more polymers selected from the group consisting of modified polysaccharides having a weight average molecular weight of about from about 700,000 to about 1,200,000. 
     
     
       133. The water-based drilling fluid of  claim 124  having a density of about 7.9 lb./gal. or more. 
     
     
       134. A water-based drilling fluid comprising:
 an aqueous base comprising a concentration of about 20 vol. % or less non-toxic water emulsifiable material as an internal phase; 
 a blend of water soluble polymers comprising from about 10 wt. % to about 90 wt. % modified polysaccharide and from about 10 wt. % to about 90 wt. % synthetically modified starch; and, 
 an amount of surfactant in association with said Water soluble polymer, said surfactant being selected from the group consisting of alkyl sulfates, alkyl ether sulfates, alkyl sulfonates, ethoxylated esters, ethoxylated glycoside esters, alcohol ethers, and phosphated esters comprising about 8 to about 18 carbon atoms, alkali metal salts thereof, and combinations thereof; 
 wherein said quantity, said amount, and said association provide said water based drilling fluid with effective rheology and fluid loss control properties comprising a low shear rate viscosity of about 70,000 cP or more upon exposure to 0.3 rpm, measured with a Brookfield viscometer at 75° F. 
 
     
     
       135. The water-based drilling fluid of  claim 134  wherein said surfactant is selected from the group consisting of alkyl sulfates and alkyl ether sulfates. 
     
     
       136. The water-based drilling fluid of  claim 134  wherein said fluid consists essentially of additives other than a solid bridging agent. 
     
     
       137. The water-based drilling fluid of  claim 134  wherein said effective fluid loss control properties comprise a fluid loss of about 5 ml./30 min. or less using the standard dynamic filtration fluid loss test. 
     
     
       138. The water-based drilling fluid of  claim 134  wherein said surfactant is effective to emulsify said water emulsifiable material and to produce emulsion droplets having an average diameter of about 30 microns or less. 
     
     
       139. The water-based drilling fluid of  claim 134  wherein said surfactant is effective to emulsify said water emulsifiable material and to produce emulsion droplets having an average diameter of about 20 microns or less. 
     
     
       140. The water-based drilling fluid of  claim 134  having a density of about 7.9 lb./gal. or more. 
     
     
       141. A water-based drilling fluid comprising:
 an aqueous base comprising a concentration of about 20 vol. % or less non-toxic water emulsifiable material as an internal phase; 
 a blend of water soluble polymers comprising synthetically modified starch and from about 40 wt. % to about 60 wt. % modified polysaccharide; and, 
 an amount of surfactant selected from the group consisting of alkyl sulfates and alkyl ether sulfates in association with said water soluble polymer; 
 wherein said quantity, said amount, and said association provide said water based drilling fluid with effective rheology and fluid loss control properties comprising a low shear rate viscosity of about 70,000 cP or more upon exposure to 0.3 rpm, measured with a Brookfield viscometer at 75° F. 
 
     
     
       142. The water-based drilling fluid of  claim 141  wherein said fluid consists essentially of additives other than a solid bridging agent. 
     
     
       143. The water-based drilling fluid of  claim 141  wherein said effective fluid loss control properties comprise a fluid loss of about 5 ml./30 min. or less using the standard dynamic filtration fluid loss test. 
     
     
       144. The water-based drilling fluid of  claim 141  wherein said concentration is from about 2 to about 20 vol. %. 
     
     
       145. The water-based drilling fluid of  claim 141  wherein said surfactant is effective to emulsify said water emulsifiable material and to produce emulsion droplets having an average diameter of about 30 microns or less. 
     
     
       146. The water-based drilling fluid of  claim 141  wherein said surfactant is effective to emulsify said water emulsifiable material and to produce emulsion droplets having an average diameter of about 20 microns or less. 
     
     
       147. The water-based drilling fluid of  claim 141  having a density of about 7.9 lb./gal. or more. 
     
     
       148. A water-based drilling fluid comprising:
 an aqueous base comprising a concentration of about 20 vol. % or less non-toxic water emulsifiable material as an internal phase; 
 about 2 lb./bbl. or more water soluble polymer comprising about 50/50 wt. % modified xanthan polysaccharide and synthetically modified starch; and, 
 about 0.2 lb./bbl. or more surfactant selected from the group consisting of alkyl sulfates and alkyl ether sulfates in association with said water soluble polymer; 
 wherein said water soluble polymer, said surfactant, and said association provide said water-based drilling fluid with effective rheology and fluid loss control properties. 
 
     
     
       149. The water-based drilling fluid of  claim 148  wherein said effective rheology and fluid loss control properties comprise a low shear rate viscosity of about 70,000 cP or more upon exposure to 0.3 rpm, measured with a Brookfield viscometer at 75° F. 
     
     
       150. The water-based drilling fluid of  claim 148  wherein said concentration is from about 2 to about 20 vol. %. 
     
     
       151. The water-based drilling fluid of  claim 148  wherein said fluid consists essentially of additives other a solid bridging agent. 
     
     
       152. The water-based drilling fluid of  claim 148  wherein said effective fluid loss control properties comprise a fluid loss of about 5 ml./30 min. or less using the standard dynamic filtration fluid loss test. 
     
     
       153. The water-based drilling fluid of  claim 148  wherein the quantity of water-soluble polymer is from about 2 lb./bbl to about 7.5 lb./bbl.